1. Field of Invention
The invention relates generally to wavelength-converted light emitting devices.
2. Description of Related Art
Light emitting devices including light emitting diodes are well known solid state devices that can generate light having a peak wavelength in a specific region of the light spectrum. LEDs are typically used as illuminators, indicators, and displays. LEDs based on the III-nitride materials system have been developed that can efficiently emit light in a relatively narrow band around a peak wavelength in the blue to UV range of the spectrum. Since blue-UV light has a higher photo energy relative to other colors of visible light, such light generated by III-nitride LEDs can be readily converted to produce light having a longer wavelength. It is well known in the art that light having a first peak wavelength (xe2x80x9cprimary lightxe2x80x9d) can be converted into light having a longer peak wavelength (xe2x80x9csecondary lightxe2x80x9d) using a process known as luminescence. The luminescence process involves absorbing the primary light by a photoluminescent phosphor material, which excites the atoms of the phosphor material, and emits the secondary light. The peak wavelength and the band of wavelengths around it (in short wavelength) of the secondary light will depend on the phosphor material. The type of phosphor material can be chosen to yield secondary light having a particular peak wavelength. Needed in the art are wavelength-converting materials (wavelength converters) that efficiently convert light in desired wavelength ranges and can withstand the same operating temperatures as the III-nitride light emitting devices.
In accordance with embodiments of the invention, a device includes a semiconductor light emitting device and a wavelength-converting material comprising Srxe2x80x94SiON:Eu2+. The Srxe2x80x94SiON:Eu2+ wavelength-converting material absorbs light emitted by the light emitting device and emits light of a longer wavelength. In some embodiments, the Srxe2x80x94SiON:Eu2+ wavelength-converting material is combined with a red-emitting wavelength-converting material and a blue light emitting device. In some embodiments, the Srxe2x80x94SiON:Eu2+ wavelength-converter is combined with a red-emitting wavelength-converter, a blue-emitting wavelength-converter, and a UV light emitting device.
The use of Srxe2x80x94SiON:Eu2+ as a green wavelength-converting material offers several advantages including high chemical and thermal stability, enhanced color rendering in white devices due to a relatively wide emission band, and potentially inexpensive synthesis.
The designator Srxe2x80x94SiON:Eu2+ is used here and in the following for materials of the general formula (Sr1xe2x88x92axe2x88x92bCabBac)SixNyOz:Eua (a=0.002-0.2, b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5, z=1.5-2.5).